N-Phosphonomethylglycine (“glyphosate”) is a well-known, post-emergent, foliar-applied herbicide. When glyphosate formulations are applied to green leaves or stems, glyphosate moves through the plant so the entire plant dies. Glyphosate works by disrupting a plant enzyme, EPSP synthase, involved in the production of amino acids that are essential to plant growth. Because the enzyme is not present in humans or animals, glyphosate has very low toxicity to humans or animals.
Glyphosate is typically formulated and applied in the form of a water-soluble agriculturally acceptable salt, preferably as a monobasic salt. The most widely employed salt of glyphosate is the isopropylamine (IPA) salt. The salts of glyphosate are generally prepared by partial or complete neutralization of the acid with an appropriate base. Glyphosate salt formulations are provided in concentrate, dilute (ready to use) and solid (granulate) forms.
Surfactants are employed as adjuvants in glyphosate salt formulations to enhance herbicidal effectiveness. Surfactants help the formulations adhere to the surfaces of leaves and thus enhance penetration. The surfactant may be blended with the glyphosate salt in the concentrate or solid forms or may be added by the user to the diluted spray solution. A wide variety of surfactants have been taught as suitable for use, and cationic surfactants, in particular, have been widely used. See, for example, the exhaustive list of surfactant types taught in U.S. Pat. Nos. 7,049,270 and 7,135,437.
Etheramine alkoxylates are known surfactants for glyphosate salt formulations. For example, U.S. Pat. No. 5,750,468 teaches that these compositions provide a less-irritating alternative to ethoxylated tallowamines. The reference teaches that quaternized or oxidized analogs of the etheramine alkoxylates can be used instead of the etheramine alkoxylates. The '468 patent also teaches that the etheramine alkoxylates are especially well-suited for use with IPA glyphosates and limits its examples to them. U.S. Pat. No. 6,277,788 also discloses etheramine alkoxylates in glyphosates, and explains the advantages of using monoethylamine (MEA) salts instead of IPA salts for making highly concentrated aqueous glyphosate compositions. U.S. Pat. Appl. Publ. No. 2010/0160162 suggests using a blend of an etheramine alkoxylate and a traditional tallowamine surfactant to improve herbicidal selectivity and reduce the tendency of the surfactant to cause eye irritation.
Since the initial suggestion to use etheramine alkoxylates in glyphosates (in the '468 patent), they have been listed as possible surfactant components in similar compositions, usually in combination with other surfactants. For instance, etheramine ethoxylates have been taught for use in combination with diamines or polyamines (U.S. Pat. Appl. Publ. No. 2003/0096708), alkylbetaines or alkyl(amido-alkyl)betaines (U.S. Pat. Appl. Publ. No. 2004/0224846), amidoalkylamines (U.S. Pat. Appl. Publ. No. 2010/0113274), and fatty amine oxides (U.S. Pat. Appl. Publ. No. 2009/0018018).
Despite their suggested use in glyphosates, etheramine alkoxylates are generally not miscible with glyphosate or water, and they may not be miscible with other surfactant components. On the other hand, a surfactant blend needs to have good stability in and of itself, and it also needs to impart stability to aqueous glyphosates in which it is formulated.
More recently, we described (U.S. Pat. Appl. Publ. No. 2009/0318294) high-load glyphosate concentrates comprising a fatty amine oxide, a solubilizer (e.g., polyethylene glycol), and a dialkoxylated alkylamine (e.g., a tallowamine surfactant). When the surfactant blend is combined with IPA, potassium, or mixed salt glyphosates, the resulting concentrates are storage stable and have high or no cloud points. The ability to provide such highly concentrated glyphosates, especially with a potassium glyphosate, is valuable. Etheramine alkoxylates are not taught as surfactant components.
Despite the high glyphosate concentration available by choosing a potassium glyphosate (compared with IPA and other amine salts), the K salt is notorious for incompatibility issues with a “wide range” of surfactants (see U.S. Pat. No. 7,316,990 at col. 2 and U.S. Pat. No. 7,135,437 at the paragraph bridging cols. 4 and 5). The '990 patent counsels use of monomethylamine (MMA) or dimethylamine (DMA) salts to enhance compatibility. Other references, such as U.S. Pat. Appl. Publ. No. 2003/0096708, discuss the difficulties in pouring or pumping highly concentrated mixtures of potassium glyphosates (see p. 4, paragraph [0033]).
Formulators of glyphosates frequently struggle with how to maintain high productivity while dealing effectively with heat removal. The exothermic neutralization reaction limits the pace at which glyphosates can be formulated without resort to expensive refrigeration units, and thus limits production rates. It is therefore desirable for formulations to have as high a cloud point as possible. A formulation that has a cloud point of 65° C., for instance, cannot be produced as efficiently as one having a cloud point of 80 or 90° C. because the formulator will have to decelerate the addition of caustic when the temperature approaches 65° C. On the other hand, it can be challenging to identify formulations that are highly concentrated, gel free, stable at elevated temperature, and also have high cloud points.
Interestingly, relatively little appears to be known about how the pH of aqueous glyphosate concentrates might impact the elevated temperature stability of aqueous formulations comprising the concentrates and commonly used surfactants. This is particularly true of highly concentrated potassium glyphosates. U.S. Pat. Appl. Publ. No. 2009/0018018 teaches potassium glyphosate compositions comprising a fatty amine oxide surfactant, an optional water-miscible solvent (N-methyl-2-pyrrolidone in the examples), and other surfactants that could be, e.g., an etheramine alkoxylate or a betaine. Table 1 of the '018 publication reports pH values for the potassium glyphosate plus water and surfactant of about 4.7. U.S. Pat. No. 7,049,270 teaches aqueous potassium glyphosate concentrates having a pH of 4.76 (see Example A, col. 72). U.S. Pat. Appl. Publ. No. 2011/0105328 teaches potassium glyphosate concentrates having a pH range from 5.5 to 11 (see paragraph [0015]). U.S. Pat. Appl. Publ. No. 2011/0009269 reports pH values of 4.5 to 5.0 for an aqueous isopropylamine (IPA) glyphosate concentrate, but alkali metal glyphosates are not discussed. U.S. Pat. Appl. Publ. No. 2010/0113274 teaches the value of amidoamines for enhancing the compatibility of other surfactants (e.g., etheramines, fatty amine oxides) in blends of potassium and monoethanolamine glyphosates. Table 11 (p. 22) lists formulation pH values of about 4.6. U.S. Pat. No. 6,767,863 (Ex. 1) indicates a pH of 4.58 for an IPA glyphosate formulation containing a tallowamine ethoxylate. U.S. Pat. No. 6,475,953 lists pH values of 5 to 7 for IPA or sodium glyphosate formulations that contain soy lecithin and other components (see Table 2a). Thus, although pH is reported for various formulations in these references, there appears to be little or no attempt to control pH to achieve a performance benefit.
U.S. Pat. Appl. Publ. No. 2010/0331182 describes high-strength concentrates of glyphosate and dicamba salts, including potassium salts, for which the pH is adjusted between 6.0 and 8.0 (abstract, Table 1). High strength is achieved provided that a mixture of glyphosate and dicamba salts is used and pH is kept within the target range. U.S. Pat. No. 7,223,718 teaches to adjust pH to 7.0 to 8.5 to achieve a single-phase concentrate comprising a glyphosate di-salt and an enhancement agent.
In sum, the industry would benefit from improved alkali metal glyphosate compositions that are highly concentrated yet have good elevated temperature stability. Of particular interest are compositions based on etheramine alkoxylates, which are less irritating than tallowamine ethoxylates. Also needed are surfactant blends useful in the glyphosate formulations that do not gel or phase separate during storage. Ideally, a variety of surfactants could be used with the etheramine alkoxylates while avoiding the compatibility problems that previously discouraged formulators from opting for alkali metal glyphosates in highly concentrated compositions. Formulators would welcome glyphosate compositions that have, in addition to the other attributes discussed above, high cloud points to allow formulation at relatively high temperatures and without the need for expensive refrigeration.